Vasoactive intestinal peptide (VIP) is a smooth muscle relaxant/bronchodilator which regulates airway mucus secretion and has anti-allergic and anti-inflammatory properties. Recent studies have resulted in the discovery of an analog of VIP which possesses enhanced metabolic stability and has increased receptor-binding properties. This VIP analog is the subject of a co-pending U.S. patent application Ser. No. 08/308,729.
To date, this VIP analog has been prepared using solid phase synthesis. The solid phase synthesis includes attaching an alpha-amino acid, protecting with, for example t-butyloxycarbonyl (Boc), by ester linkage, to a chloromethylated resin or a hydroxymethyl resin. More amino acids are added sequentially to the resin. The alpha amino Boc protection is removed under acidic conditions and the subsequent protected amino acids are coupled stepwise to obtain an intermediate, protected peptide-resin. Blocking groups are removed and the peptide is cleaved from the resin through multiple hydrogen fluoride cleavage reactions. Purification of the peptides occurs in two stages, a) size exclusion gel chromatography and b) preparative high performance liquid chromatography (HPLC). This multistep process is time consuming and results in inefficient recovery of the target peptide.
It is thus an object of the present invention to provide a relatively simple, more efficient and economic procedure for the synthesis of the VIP analog.